[Reg 5.12.0->5.12.1] QCombobox popup is not showing largest string in list properly

QCombobox popup is not showing the largest entry in list properly. Say, we have 5 entries in combobox as below and "Process Group" has maximum no. of characters

    mp_box->addItem( "Name", 1 );
    mp_box->addItem( "Threads", 2 );
    mp_box->addItem( "System Tree", 3 );
    mp_box->addItem( "Process Group", 4 );
    mp_box->addItem( "Number", 5 );

In popup, "Process Group" is shown as "Process",i.e "Group" is trimmed from it. This is working fine with 5.12.0 on Mac and fine with all versions on Windows.
Please refer to attached project and snapshots.